1. Field of the Invention
The present invention relates to a method for controlling and/or regulating an electric drive in hybrid vehicles, in particular, for entry-level hybridizations having voltages lower than 60 V. Other aspects of the present invention relate to a computer program for carrying out the method according to the present invention, an electrical storage medium for storing such a computer program, as well as a control and/or regulating device configured for carrying out the method according to the present invention.
2. Description of the Related Art
Within the framework of the public debate about CO2, as well as steadily rising fuel prices, systems for reducing fuel consumption and, thus, CO2 emissions are gaining in importance. Against this background, a hybridization of the drivetrain is becoming increasingly important.
One of the inherent objectives of hybrid vehicles is to reclaim (recuperate) the kinetic energy released during braking, respectively the potential energy released during downhill driving. They may be utilized, for example, for supplying power to the vehicle electrical system, thereby substantially influencing fuel consumption.
If the electrical machine also permits a motor operation through the use of a power inverter, then the driving torque of the combustion engine can be increased by an electric moment (boost), for example, to enhance drivability. In addition, if more energy is recovered by recuperation than is needed for supplying the vehicle electrical system or for the boost function, for example, then it is also possible to selectively reduce the driving torque of the combustion engine and to compensate for the same through an electric moment.
The fuel consumption can be further reduced by such a load-point shift. Thus, hybridization of the drivetrain requires a suitable electrical machine and a suitable energy accumulator, such as a lithium-ion battery, as a power battery, as well as an appropriate control strategy.
In hybrid vehicles, the electric drive can either be used as a source of motive power to assist the combustion engine, or it can be used regeneratively, for example, to recapture braking energy. However, if the power battery has a low state of charge or, generally, a poor state, for example, due to temperature or aging, a regenerative operation can be necessary even outside of the braking phases. In this case, the electric drive is not driven by the kinetic, respectively potential energy of the vehicle. Rather, it must be driven by the combustion engine which requires using additional fuel to produce current to charge the power battery, respectively to supply the vehicle electrical system. In this case, the regenerative operation leads to an increase in fuel consumption.
To regulate the operating modes of the electric drive, thus, both of the motive and regenerative power thereof, various energy management strategies are possible. The aim of these strategies can be to adjust a setpoint state of charge. Following a recuperation phase and, thus, a state of charge greater than the setpoint state of charge, this leads to a boost phase being introduced until the setpoint state of charge is adjusted. However, if the driver requires an electric assist for an extended period of time, then, following this boost phase, the attempt would likewise be made to restore the setpoint state of charge as quickly as possible by a regenerative operation of the electric drive, in this case, using fuel to drive the electric drive in regenerative mode. The aim of readjusting the setpoint state of charge as fast as possible leads to a cycling and thus aging of the power battery.
Published German Patent Application document DE 103 46 213 A1, for example, describes a method for regulating the state of charge of an energy accumulator in the case of a vehicle having a hybrid drive where the state of charge of the energy accumulator is regulated by a charge controller as a function of the driving speed of the vehicle.